This invention relates to a waste disposal problem and to the preparation of organic polysulfide polymers by using heavy residues derived from the manufacture of vinyl chloride.
Industrially, vinyl chloride is prepared according to numerous processes which use mainly ethylene, acetylene or a mixture of ethylene and acetylene as starting materials. Whatever the type of reaction used, chlorination or oxychlorination, in processes using ethylene there is formed the intermediate 1,2 dichloroethane (also called ethylene dichloride or EDC) which is then pyrolysed or dehydrochlorinated in alkaline medium in order to obtain vinyl chloride. Mixtures of organic chlorinated products which are the heavy residues of the manufacture of vinyl chloride are obtained as still bottoms during the purification by distillation of dichloroethane (see for example Kirk Othmer Encyclopedia of Chemical Technology 2nd edition Vol. 5 p. 175, l 26 and Riegel's Handbook of Industrial Technology page 784 FIG. 25.9). Heavy residues are also obtained as still bottoms from the vinyl chloride fractionation, optionally after recovering of dichloroethane by distillation, (see for example Kirk Othmer Encyclopedia of Chemical Technology 2nd Edition Vol. 5 p. 175 l 40). The term "heavy residues" is thus used to designate mixtures of chlorinated compounds which are liquids at normal pressure, which are recovered as said still bottoms in plants producing vinyl chloride and are usually discarded.
The analysis of numerous heavy residues obtained from several plants has shown that the chlorinated aliphatic products having a short carbon chain constitute the predominant part of these mixtures. In particular, the total amount of 1,2-dichloroethane, 1,1,2-trichloroethane, 1,1,2,2-tetrachloroethane and 1,1,1,2-tetrachloroethane generally ranges between 40 and 70% by weight based on the whole quantity of the chlorinated compounds, but this amount may be greatly increased and may be as high as 90% by weight under extreme plant operating conditions. The respective percentages of each of these four constituents may greatly vary, and for example the percentage of 1,2-dichloroethane may be comprised within 2 and 70% by weight based on the weight of the heavy residues.
The other products which are in the residues are different aliphatic compounds having 1 to 4 carbon atoms and aromatic and cycloaliphatic compounds. Among these aliphatic compounds, the following products generally occur: chloroform, carbon tetrachloride, chloroethanol, chloromethylether, chloral, 1,1-dichloroethane, trichloroethylene, tetrachloroethylene, chloropropanes, chloropropenes, dichloropropanes, dichloropropenes, trichloropropenes, chloroprene, and its dimer, chlorobutenes, dichlorobutenes and dichlorobutanes. Among aromatic and cycloaliphatic compounds, following products can occur: chlorobenzene, dichlorobenzenes, chloroxylenes (xylyl chloride), trimethylbenzenes, dichlorocyclohexadienes. Actually, the relative percentages of these compounds can be greatly varied, because they depend on numerous factors: in particular the purity of used ethylene for the preparation of dichloroethane, the operation of the vinyl chloride plant, and the origin of the chlorine or hydrogen chloride used for chlorination or oxychlorination. Brominated and chlorobrominated organic compounds such as bromochloroethane, bromochloroethylene, dibromoethane, dibromoethylene or mineral chloride such as hydrogen chloride or molecular chlorine can be also found in these residues.
According to the present invention the heavy residues are defined by the chlorine content which is of an organic origin and which is contained in the heavy residues, the content of chlorine which is of a mineral origin being of minor importance and, in any case, being lower than 1% by weight. Analyses of numerous residues have shown that the amount of chlorine of organic origin (in order to simplify the term organic chlorine is used hereunder to designate the chlorine having an organic origin) ranges between 55 and 80% by weight based on the weight of the heavy residues.
Heretofore, these heavy residues had never been commercially utilized and constituted a serious waste disposal problem. Since polyvinylchloride is manufactured up to now they were stored and destroyed by combustion in the presence of fuel-oil, on special boats off shore. This type of treatment, however, has many disadvantages; in particular it increases the cost of the vinyl chloride production on the one hand, and increases atmospheric pollution owing to hydrogen chloride formed by combustion on the other hand.